U.S. patent number 4,157,998 [Application Number 05/864,035] was granted by the patent office on 1979-06-12 for method of producing a cement mortar with good stability in a fresh condition and a method using this mortar as a binding agent of producing a lightweight aggregate concrete with a high aggregate content.
This patent grant is currently assigned to AB Bofors. Invention is credited to Leif Berntsson, Bengt Hedberg, Soren Karlsson, Olof Magnusson.
United States Patent |
4,157,998 |
Berntsson , et al. |
June 12, 1979 |
Method of producing a cement mortar with good stability in a fresh
condition and a method using this mortar as a binding agent of
producing a lightweight aggregate concrete with a high aggregate
content
Abstract
The present invention relates to a method of producing a cement
mortar with a density of 1200-2000 kg/m.sup.3 with good stability
in a fresh condition. According to the invention, this good
stability in the mortar is achieved through an extremely fine-pored
structure initiated by fine-particle material with certain fixed
properties added to the fresh mortar. The invention also comprises
a method, using said mortar as a binding agent, of producing a
lightweight aggregate concrete with an aggregate content of 45-80
percent by volume and a density below 1400 kg/m.sup.3 where the
aggregate material has a particle density of less than 1200
kg/m.sup.3 and the mortar entirely fills out the space between the
aggregate particles.
Inventors: |
Berntsson; Leif (Goteborg,
SE), Hedberg; Bengt (Goteborg, SE),
Karlsson; Soren (Karlskoga, SE), Magnusson; Olof
(Karlskoga, SE) |
Assignee: |
AB Bofors (Bofors,
SE)
|
Family
ID: |
20329840 |
Appl.
No.: |
05/864,035 |
Filed: |
December 23, 1977 |
Foreign Application Priority Data
|
|
|
|
|
Dec 23, 1976 [SE] |
|
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7614518 |
|
Current U.S.
Class: |
524/5; 106/668;
106/672; 106/679; 106/692; 524/8 |
Current CPC
Class: |
C04B
20/1018 (20130101); C04B 24/26 (20130101); C04B
24/36 (20130101); C04B 28/02 (20130101); C04B
20/1018 (20130101); C04B 16/04 (20130101); C04B
28/02 (20130101); C04B 14/06 (20130101); C04B
16/04 (20130101); C04B 24/32 (20130101); C04B
28/02 (20130101); C04B 14/06 (20130101); C04B
16/04 (20130101); C04B 24/26 (20130101); C04B
28/02 (20130101); C04B 14/06 (20130101); C04B
16/04 (20130101); C04B 24/36 (20130101); C04B
2103/304 (20130101) |
Current International
Class: |
C04B
20/10 (20060101); C04B 28/02 (20060101); C04B
20/00 (20060101); C04B 28/00 (20060101); C04B
24/26 (20060101); C04B 24/36 (20060101); C04B
24/00 (20060101); C04B 007/35 () |
Field of
Search: |
;260/29.6S,42.13
;106/90,96,97 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Griffin; Ronald W.
Attorney, Agent or Firm: Pollock, Vande Sande and Priddy
Claims
We claim:
1. A method for producing a cement mortar containing cement, solid
particles and water and having finely distributed gas in the mortar
in an amount sufficient to provide said mortar with a density of
1200-2000 kg/m.sup.3 which comprises introducing into the mortar
prior to setting thereof 0.2-5.0 percent by weight based upon the
quantity of cement of a particle-shaped hydrophilic-hydrophobic
balanced product chemically inert in relation to the rest of the
mortar and consisting of substantially spherical hydrophobic
particles of 0.1-1.0 .mu.m strongly adsorbed on the surface of
which is a hydrophilic nonionic tenside in amount of 0.1-5.0
percent by weight based on the total weight of said product.
2. The method of claim 1 which comprises introducing into said
mortar a particle-shaped product of a homopolymer or copolymer of
styrene, or at least one ester of acrylic or methacrylic acid, or
copolymer of styrene and said ester wherein said ester has the
formula: ##STR2## in which R.sub.1 =H or CH.sub.3 and R.sub.2 =an
alcohol radical with 1-8 carbon atoms with a particle size of
0.2-0.6 .mu.m having adsorbed on its surface 0.1-3.0 percent by
weight of nonionic tenside.
3. The method of claim 2 wherein said ester is methyl acrylate or
ethyl acrylate or propyl acrylate or butyl acrylate or hexyl
acrylate or 2-ethyl hexyl acrylate or methyl methacrylate or ethyl
methacrylate or butyl methacrylate or hexyl methacrylate or 2-ethyl
hexyl methacrylate or mixtures thereof.
4. The method of claim 1 which comprises introducing into said
mortar a particle-shaped product of a copolymer of vinylidene
chloride and acrylic acid ester or a homopolymer of vinylidene
chloride having adsorbed on its surface of 0.1-3.0 percent by
weight of nonionic tenside.
5. The method of claim 1 which comprises introducing into said
mortar a particle-shaped product of a copolymer of
styrene-butadiene having adsorbed on its surface 0.1-5.0 percent by
weight of nonionic tenside.
6. The method of claim 1 which comprises introducing into said
mortar a particle-shaped product of polyethylene with a particle
size of 0.2-0.6 .mu.m.
7. The method of claim 1 wherein said spherical hydrophobic
particles are of a natural product.
8. The method of claim 7 wherein said natural product is asphalt
having a particle size of 0.1-0.8 .mu.m.
9. The method of claim 1 which comprises initiating drawing in of
finely distributed air into said mortar by introducing said
particle-shaped product.
10. The method of claim 1 wherein said solid particles are
sand.
11. The method of claim 1 wherein said cement is Portland
cement.
12. The method of claim 1 wherein said cement is aluminate
cement.
13. The method of claim 1 wherein said cement is slag cement.
14. A cement mortar obtained by the method of claim 1.
15. A method for producing a light aggregate concrete of density
less than 1400 kg/m.sup.3 from a cement mortar comprised of cement,
solid particles, and water and having finely distributed gas in the
mortar in an amount sufficient to provide said mortar with a
density of 1200-2000 kg/m.sup.3, and 45-80 percent by volume of a
light aggregate material with a particle density of less than 1200
kg/m.sup.3 wherein the cement mortar entirely fills out the space
between the aggregate particles which comprises initiating of
distribution of said finely distributed gas in said mortar by
incorporating prior to admixing said light ballast with said cement
mortar 0.2-5.0 percent by weight based upon the amount of said
cement in said mortar of a particle-shaped hydrophilic-hydrophobic
balanced product chemically inert in relation to the rest of said
mortar and consisting of substantially spherical hydrophobic
particles of 0.1-1.0 .mu.m strongly adsorbed on the surface of
which is a hydrophilic nonionic tenside in amount of 0.1 to 5.0
percent by weight based on the total weight of said product.
16. The method of claim 15 which comprises introducing into said
mortar a particle-shaped product of a homopolymer or copolymer of
styrene, or at least one ester of acrylic or methacrylic acid, or
copolymer of styrene and said ester wherein said ester has the
formula: ##STR3## in which R.sub.1 =H or CH.sub.3 and R.sub.2 =an
alcohol radical with 1-8 carbon atoms with a particle size of
0.2-0.6 .mu.m having adsorbed on its surface 0.1-3.0 percent by
weight of nonionic tenside.
17. The method of claim 16 wherein said ester is methyl acrylate or
ethyl acrylate or propyl acrylate or butyl acrylate or hexyl
acrylate or 2-ethyl hexyl acrylate or methyl methacrylate or ethyl
methacrylate or butyl methacrylate or hexyl methacrylate or 2-ethyl
hexyl methacrylate or mixtures thereof.
18. The method of claim 15 which comprises introducing into said
mortar a particle-shaped product of a copolymer of vinylidene
chloride and acrylic acid ester or a homopolymer of vinylidene
chloride having adsorbed on its surface of 0.1-3.0 percent by
weight of nonionic tenside.
19. The method of claim 15 which comprises introducing into said
mortar a particle-shaped product of a copolymer of
styrene-butadiene having adsorbed on its surface 0.1-5.0 percent by
weight of nonionic tenside.
20. The method of claim 15 which comprises introducing into said
mortar a particle-shaped product of polyethylene with a particle
size of 0.2-0.6 .mu.m.
21. The method of claim 15 wherein said spherical hydrophobic
particles are of a natural product.
22. The method of claim 21 wherein said natural product is asphalt
having a particle size of 0.1-0.8 .mu.m.
23. The method of claim 15 which comprises initiating drawing in of
finely distributed air into said mortar by introducing said
particle-shaped product.
24. The method of claim 15 wherein said solid particles are
sand.
25. A light aggregate concrete obtained by the method of claim
15.
26. A method for producing a hardened cement mortar wherein the
major portion of all pores thereof are 5-30 .mu.m containing
cement, solid particles and water and having finely distributed gas
in the mortar in an amount sufficient to provide said mortar with a
density of 1200-2000 kg/m.sup.3 which comprises introducing into
the mortar prior to setting thereof 0.2-5.0 percent by weight based
upon the quantity of cement of a particle-shaped
hydrophilic-hydrophobic balanced product chemically inert in
relation to the rest of the mortar and consisting of substantially
spherical hydrophobic particles of 0.1-1.0 .mu.m strongly adsorbed
on the surface of which is a hydrophilic nonionic tenside in amount
of 0.1-5.0 percent by weight based on the total weight of said
product, and allowing the composition to harden.
27. A cement mortar comprising cement, solid particles, water,
finely distributed gas in an amount to provide said mortar with a
density of 1200-2000 kg/m.sup.3, and 0.2-5.0 percent by weight
based upon the quantity of said cement of a particle-shaped
hydrophilic-hydrophobic balanced product chemically inert to the
rest of the mortar and consisting of substantially spherical
hydrophobic particles of 0.1-1.0 .mu.m strongly adsorbed on the
surface of which is a hydrophilic nonionic tenside in amount of
0.1-5.0 percent by weight based on the total weight of said
product.
28. A light aggregate concrete of density less than 1400 kg/m.sup.3
from a cement mortar comprised of cement, solid particles, and
water and having finely distributed gas in the mortar in an amount
sufficient to provide said mortar with a density of 1200-2000
kg/m.sup.3, and 45-80 percent by volume of a light aggregate
material with a particle density of less than 1200 kg/m.sup.3
wherein the cement mortar entirely fills out the space between the
aggregate particles and 0.2-5.0 percent by weight based upon the
amount of said cement in said mortar of a particle-shaped
hydrophilic-hydrophobic balanced product chemically inert in
relation to the rest of said mortar and consisting of substantially
spherical hydrophobic particles of 0.1-1.0 .mu.m strongly adsorbed
on the surface of which is a hydrophilic nonionic tenside in amount
of 0.1 to 5.0 percent by weight based on the total weight of said
product.
Description
BACKGROUND OF THE INVENTION
The word cement is used here in its wider sense, and thus
comprises, in addition to Portland cement, hydraulic binding agents
such as aluminate cement, slag cement etc.
According to the information sheet B8:1973 published by
"Byggforskningen" ("Construction Research") and entitled
"Betongtillsatsmedel" ("Concrete Additives") hitherto known
concrete additives can be divided up into a plurality of different
groups, of which the first two are "Luftporbildande tillsatsmedel"
("Air-entraining additives") and "Vattenreducerande (plasticerande)
tillsatsmedel" ("Water-reducing (plasticizing) additives").
The present invention relates to these two groups, although it can
still not be referred entirely to one or the other or to both.
A fresh cement-based binding agent mixture (cement mortar or
concrete mass) consists of solid particles, water and air. The
cement-bonded concrete, which from the point of view of volume has
the largest share within the construction industry, substantially
consists of approx. 100 liters of cement, 200 liters of water, 650
liters of stone material, all of which with a diameter of less than
4 mm is usually designated sand, and the remainder stone, and 50
liters of air, counted on 1000 liters of fresh concrete mass. Of
the 200 liters of water which is required in order to make it
possible to process the mixture, approx. 60 liters is bonded
chemically in the hardened cement paste, while the remaining
quantity is bonded physically as gel and capillary water.
The solid particles comprised in the cement mortar or the concrete
consist of aggregate, i.e. stones and sand of various fractions,
the actual cement grains, and hydratation products precipitated in
water. The cement grains react with parts of the water mixture to
form a hydratation product which consists of a colloidal glue, the
cement gel. The remaining water and the air are distributed in the
basic mass formed by cement gel and aggregate. In the fresh mortar,
the water will be found in the form of menisci in the cavities
between solid cement and aggregate particles in their vicinity,
while the air, in turn, forms pores between these particles and the
water menisci. The particle size of the previously mentioned
precipitated hydration products is within the Angstrom range, while
the mean grain size of the cement grains is approx. 5 .mu.m. The
sand and other aggregate material, finally, can have a particle
size from approx. 0.1 mm up to one or a few centimeters. If no
special measures are taken, a fresh cement mortar will have an air
content of between 1.5 and 3.5 percent by volume. In the hardened
cement-bonded mass, there are both air and water-filled pores. In
addition to these pores, the size of which in a well packed
cement-bonded mass is between 10.sup.-1 and 1 mm, also so-called
capillary pores are formed, with a pore size of 10.sup.-4 to
10.sup.-2 mm and in the hardened cement gel so-called gel pores
with a pore size of approx. 10.sup.-6 mm.
The size and quantity of the gel pores can be influenced only to a
little extent via the water content of the original mixture, while
on the other hand, the capillary pores are determined by the water
cement ratio. A great many different ways of increasing the air
pore content in fresh cement or concrete mass is described in
literature.
In the Construction Research Brochure it is stated that such air
entraining agents increase the total air content in the fresh
cement or concrete mixture, and also cooperate towards a more
uniform distribution of the air pores in the basic mass, at the
same time as, to a certain extent, one obtains an increase of the
content of small air bubbles, i.e. bubbles with a diameter of
between 0.05 and 0.5 mm. As long as these finely distributed air
bubbles exist, this gives the fresh mass an improved stability,
which also contributes towards less water separation. If it is
primarily desired to improve the stability of the fresh mass,
without any requirements other than a certain air content,
according to generally known technology, it is sufficient to dose
for an air content of 3.0-4.0%. An increased admixture of air also
has a certain improving effect on the flow of the fresh mass, as
the air pores give rise to less friction between the solid
particles in the mass, and thereby make this easier to work with.
However, high contents of solid fine material at an increased air
content are considered to give a tough, sticky concrete. As the
consistency of a cement or concrete mass as a rule is used as a
basis, the water content of the mixture can usually be lowered by
an admixture of an air-entraining agent. According to a rule of
thumb given in literature, it should be possible to reduce the
water content in fresh cement mortar, with unchanged consistency,
by one-half of the air content increase achieved through the
addition of an air-entraining agent. Together with the previously
mentioned reduced water separation, an increase of the quantity of
fine air pores in the basic mass also involves that large aggregate
particles are not as easily separated out of the fresh mixture.
However, the changes in consistency hereby achieved are
comparatively limited, as they are directly dependent on the
quantity of stable air which in this way can be drawn into the
mass. However, the perhaps most common reason for adding
air-entraining agent is that it is desired to make the hardened
mass more resistant to frost, since the cavities achieved by the
addition of air-entraining agent will be available as expansion
chambers for other water existing in the pore system when this
increases its volume in connection with its freezing. The walls of
the pores are hereby prevented from being broken when the ambient
temperature falls below the feezing point. An air pore volume of
approx. 5 percent by volume is considered to give a maximum
resistance to frost, and this can comparatively easily be achieved.
As long as the strength of any aggregate material is greater than
that of the stiffened cement paste, the strength of this will
determine the strength of the mass. The properties of the hardened
mass will to a very great exgent be dependent on the water and air
content of the original mixture. A plurality of different materials
has been used as air-entraining agents, such as saponified resins,
alkyl aryl sulfonate, calcium ligno sulfonate and hydroxy ethyl
cellulose, in combination with tensides. From the point of view of
functioning, these additives are based upon the fact that with the
aid of the foaming agents comprised in them, a more or less stable
foam is built up, with the aid of which increased quantities of air
can be introduced into a fresh cement or concrete mass. The air
pores hereby initiated will substantially be of the magnitude of
0.1-1 mm. These additives make it possible to manufacture cement
mortar and concrete with a reduced density. However, foam bubbles
of this size have poor own strength, and the pore system hereby
built up can therefore collapse before the cement bonding agent has
had time to harden. This applies particularly when it is desired to
introduce large quantities of air. The mainly hydrophilic nature of
the additives can also contribute towards an increased water
absorption in the hardened mass. Through the addition of only
tensile (either anion active or non-ion active) it is also
possible, within certain limits, to change both the consistency and
the quantity of the air comprised in a fresh cement composition.
However, regardless of the type of tenside which has been used,
this procedure has proved to be very sensitive as regards the
quantity of tenside added, which at the most should comprise one or
a few per mille of the entire mixture. The tensides used in this
connection are highly effective, and can rapidly give a great
quantity of air bubbles. However, the stability of these varies
considerably. As a rule, anion active tensides lower the surface
tension drastically when small quantities are added, while the
non-ion active tensides have a somewhat lesser effect with one and
the same concentration. With these two types of tensides, however,
particularly at an over-dosing, the air bubbles generated from the
beginning are rapidly recombined, i.e. they join together to form
larger units. Particularly with the anion-active tensides, this
recombination can take place to such an extent that air leaves the
system, and a collapse occurs, i.e. the fresh mixture shrinks.
Certain non-ion active tensides show considerably better stability,
and therefore a greater tolerance towards over-dosing, but it is
very noticeable, however, that recombination increases at e.g. more
intensive stirring. Nor is it possible through regulating of such
parameters as the choice of type of stirrer, the quantity of
tenside added, and the intensity of the stirring, to control the
quantity of air mixed in or the size of the air pores, which will
vary between 0.1 and several mm.
When additives of the kind described above are used, the intention
can be to mix in air, or that it is desired not to add more air to
a concrete mixture. Through the choice of type of tenside and the
quantity added, both of these effects can be achieved. In the
Swedish published application No. 333 113, it is described how,
through the addition of various tensides plus a styrene acrylate
dispersion, the workability and flow of a concrete mixture
increases. As this addition permits a considerable reduction of the
water cement ratio of the fresh mixture, the hardened concrete
mixture can be given a more compact structure and, consequently,
increased strength. It is said that the dispersion in question,
notwithstanding a high content of tensides, does not have any
foaming capability. It is also particularly pointed out that it
does not give rise to any formation of air pores. However, the
quantity of tensides added and the quantity of acrylonitrile
comprised in the polymer will make the hardened concrete highly
hydrophilic.
In the Swiss patents Nos. 493,438 and 515,862 cement and concrete
additives are described consisting of polymer or natural latex
dispersions containing water, to which in addition to polymer
components and emulsifiers, also an anti-foaming agent has been
added.
Further, in the U.S. Pat. No. 3,819,391, an air-entraining cement
additive has been described, consisting of a free-flowing flaky
solid product containing 12.5-37.5 percent by weight of a
bituminous substance and the remainder, 87.5-62.5 percent by
weight, of a surface-active substance. In this additive, the major
portion thus consists of the surface-active substance.
The Swedish patent application 7600161-9 relates to a development
of the additive according to the above-mentioned U.S. patent, here
in the form of a powder-formed product, soluble in water, which to
40-60 percent by weight is built up of the above-mentioned
bituminous substance and a surface-active substance, while the
remaining 60-40 percent by weight consist of polyethylene oxide
resins, lignol sulfonates and diatomaceous earth. As a
surface-active agent it is said that both anion, cation and non-ion
agents can be used, but that a mixture is preferred. It is stated
that the bituminous material may be asphalt, coal tar or
derivatives thereof. In order that it may be used in this
connection, however, it is a requirement that the substance in
question shall be a liquid at room temperature. In addition to its
air-entraining function, it is said that the additive also has a
binding-retarding effect on the cement.
In the Swedish patent application No. 74.03454-7, it is also shown
how, with the aid of colloidal silica, surface-active substances
and amphiphilic substances or hydrocarbons, the consistency,
workability and uniform distribution of the fine portion of the
cement can be changed. In a table on page 6, the great importance
of the water cement ratio is shown. When, with the aid of an
additive, more air is introduced into the concrete, the water
content can be reduced at the same time. The greatest reason for
the increase in strength reported in the application must
presumably be ascribed to the reduced water content. However, it
should be possible to refer a complementary effect to the silica
which is chemically active in connection with the hardening of the
cement.
As indicated by the above-mentioned review of at least some of the
concrete additives which have previously been proposed, there is
nothing new in endeavouring to manipulate the structure of a fresh
cement composition through miscellaneous additives, which primarily
have an, albeit limited, effect of drawing in air. The fact that at
least some of these air-entraining agents have also had a tendency
to increase the content of fine air pores in the mixture is
likewise previously known. In general, however, these older types
of air-entraining agents have also given rise to large quantities
of comparatively large pores, i.e. pores with a size of 0.1-1.0 mm
and more.
SUMMARY OF INVENTION
The present invention now relates to a method of initiating an
extremely fine and uniformly pored structure in fresh cement
mortar. This special pore structure is achieved by a fine-particle
material with a certain particle size and form and with certain
defined surface properties being incorporated into the fresh
mortar. These specific properties give the material in question a
marked capability of entraining air, together with the capability
of holding the air which has been drawn in together in extremely
fine and stable bubbles, which during the working of the mortar are
distributed in this, without being recombined with each other. In
this way, an extremely fine-pored mortar is obtained. The
properties characteristic of the particle-formed material include
the fact that the individual particles show hydrophilic and
hydrophobic properties concentrated to the respective particle
surface, which in a certain way have been balanced off in relation
to each other. This combination of properties contradictory to each
other obviously makes it possible for the particles in question to
divide up large water menisci into smaller ones.
We have not been able to find any other explanation as to why a
hardened cement mortar, produced in accordance with the invention,
can show a pore structure in which the major portion of all pores
are within the size range of 5-30 .mu.m. Otherwise, large pores,
achieved by large water menisci are very common. The pore structure
of the hardened mortar has been measured in a scanning microscope.
In the fresh mortar, this can be more difficult, but if no collapse
of the pore system occurs before the hardening, the pores of the
fresh mortar correspond to the pores of the stiffened mortar, but
with the difference that part of the pores in the fresh mortar are
filled with water.
The method according to the invention thus offers a method of
producing a fresh cement mortar which, notwithstanding such an
extreme air content as up towards 40 percent by volume,
nevertheless has a very good stability. This good stability makes
its possible to mix in considerably greater quantities of aggregate
of another density into the mortar than would previously have been
possible in practice. In a mortar with less good stability, the
lightweight aggregate would have time to float up, and the really
heavy aggregate would sink to the bottom before the mortar had
hardened.
The explanation of the good stability of the mortar according to
the invention is that the surface-tension forces which prevent the
air pores in fresh mortar from collapsing under the surrounding
pressure at small pores or water menisci are considerably greater
than the corresponding conditions for the larger ones.
Another effect which is achieved with such a fine-pored mortar as
the one in question is that its workability is improved. This is
explained by the fact that the small air pores, as soon as the
adhesive forces have been overcome, will facilitate the
displacement of the solid particles in relation to each other. As a
consequence of this, the mortar will have considerably improved
pouring properties. As previously stated, the fine air pores
initiated in accordance with the invention are extremely well
anchored in the fresh mortar at atmospheric pressure, but if the
surrounding pressure is increased to such a high degree that the
surface-tension forces acting upon the pores are exceeded, the
entire structure will momentarily collapse when the fine pores,
after the adhesive forces have been exceeded, make the solid
particles so easily movable in relation to each other that it can
practically be called a sheer quicksand effect. If the structure
then collapses and the air leaves the system, a more complete
particle contact will be achieved between the cement grains,
aggregate if any, and the particle-formed material. The fine
spherical particles will then particularly facilitate the movements
of the extremely roughly-shaped cement grains in relation to each
other. Because of this effect, cement mortar produced according to
the present invention should be extremely well suited for extrusion
under high pressure through a die to form products with an
extremely high density and strength.
In a special fresh cement mortar produced in accordance with the
present invention, the structure collapsed at an increase in
pressure corresponding to 4 atmospheres overpressure.
Generally, in this connection, air pores and capability of drawing
in air are mentioned. The reason for this is that the surrounding
atmosphere in practically all cases will consist of air. If, for
any reason, this should consist of another gas, a corresponding
pore formation will be applicable. As the particle-shaped material
which, according to the present invention, is incorporated into the
mortar chiefly seems to function as nuclei for the fine pores, we
consider it to be probable that the pore structure will be about
the same with an in situ generated gas, i.e. a distribution of this
into very fine gas bubbles.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a graph of pressure strength for varying amounts of an
additive employed in the present invention in Examples 12, 13, and
14.
FIG. 2 is a graph of bulk density for varying amounts of an
additive employed in the present invention in Examples 12, 13, and
14.
FIG. 3 is a graph of water-cement ratio for varying amounts of an
additive employed in the present invention in Examples 12, 13, and
14.
DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention thus relates to a method of producing an
extremely fine-pored cement mortar by conveying comparatively large
quantities of finely distributed air to the mortar, and with the
aid of this finely distributed air by dividing up large
accumulations of water in the mortar into smaller ones. The method
according to the invention results in pores in the stiffened mortar
of the magnitude of 5-30 .mu.m. This is achieved by the
introduction into the fresh mortar of 0.2-5.0 percent by weight
counted on the cement weight of a substantially spherical,
particle-shaped fine material, which is chemically inert in
relation to the other components in the cement and which has a
particle size of 0.1-1.0 .mu.m, particularly 0.2-0.8 .mu.m, and the
surface properties of which show an adapted balance between
hydrophilic and hydrophobic properties, as this type of
particle-shaped material has proved to initiate very fine air pores
when the components in the mortar are mixed with each other. The
mixed hydrophilic and hydrophobic character of the particle-shaped
material gives the particles unique properties which makes it
possible for these to function as nuclei for dividing up large
water menisci into smaller ones. It should also be entirely obvious
that the particle-shaped material influences the adhesion within
the air pores, as these proved to have considerably better
stability than there had been reason to assume. This is
particularly shown by the little tendency of the pores towards
recombination. This is presumably concerned with the accumulation
of particle-shaped material at the phase boundaries of the pores,
which we have been able to see in a sweep electron microscope. This
particle accumulation at the phase limits involves that the inner
walls of the pores, after the hardening of the cement, will partly
consist of this material, either in a particle form or, if the
character of the particles is such that a film formation can take
place, by a more or less coherent film. The accumulation at the
pore walls should also to a certain extent be applicable to the
capillary pores. Primarily in the case of moulded products, we have
also been able to notice an accumulation of the particle-shaped
material towards the outer sides of the product. All of this
together gives a tight product which has very little water
absorption.
As previously stated, the method according to the invention
involves that rather large quantities of air are drawn into the
mortar. We therefore primarily consider the method according to the
invention to be suitable for producing cement mortar with a density
of 1200-2000 kg/m.sup.3, which for mortar with an own density of
2300 kg/m.sup.3 (without any air whatsoever enclosed) would
correspond to the air content of from about 13-14 percent by volume
up towards 40 percent by volume.
The formation of pores initiated according to the invention must
not be disturbed by a simultaneous or previous addition of foaming
agent, e.g. free tenside, as in such a case an uncontrolled foaming
would be initiated, even if the large air pores then drawn into the
cement, through the influence of the particle-shaped cement are
broken down into finer pores, will have a disturbing effect on the
structure desired.
The particle-shaped material can be mixed with the cement as dry
powder before the water is added, or can be added dispersed in the
water to be mixed in. However, it is necessary to ensure that the
particle-shaped material is substantially available in the form of
separate particles, and that they do not stick together and form
large aggregates. Because of their size, corresponding to 1/50-1/5
of the cement particles, the spherical particles in question will
have their place in the empty space in the particle distribution
curve which there is in a conventional cement mortar between the
previously mentioned hydratation products released in the water and
the actual cement particles. This should be an explanation of why
the particle-shaped material does not disturb the cement structure,
but rather contributes towards an improvement of it.
When mixed into the cement mortar, the particles primarily tend to
be attracted to the nearest larger particles, i.e. the cement
particles, and there constitute the previously mentioned nuclei for
dividing up the water menisci between these cement grains
themselves and between the cement grains and the aggregate
particles.
A method of producing polymeric spherical, comparatively uniform
particles, is through emulsion polymerization, where the polymers
can be used upon acrylates, styrene, copolymer of styrene acrylate,
vinyl acetate, copolymer vinyl acetate acrylate, copolymer styrene
butadiene, vinylidene chloride or the like.
In order to obtain particles within the size range desired in the
present connection, i.e. 0.1-1.0 .mu.m, surface-active substances
are used, the hydrophilic part of which can be anion active,
non-ion active, cation active or amphoteric.
Dispersions available in the market, primarily intended for paint,
glue, or other manufacture, when tested as cement additives have
proved to involve an immediate change of the consistency of the
fresh cement mortar, caused by a noticeably increased admixture of
air. However, the effect has varied very much from case to case, at
the same time as the air bubbles mixed in have been of very
different sizes (between 0.1 and several mm). The tendency towards
recombination between the bubbles hereby initiated also proved to
be very great, at the same time as the reproducibility between
different tests with the same product was poor.
This has its explanation in the comparatively high concentration of
surface-active substances which are generally present in polymer
dispersions, and which almost always are moreover combined with the
presence of polymerizable polar substances and/or protective
colloids. In such a dispersion there are thus sufficiently high
concentrations of surface-active substances which are not
sufficiently strongly adsorbent on the polymer surface. The part of
these surface-active substances which are not adsorbed to the
polymer surface in themselves give rise to air bubbles of an
unstable character, which are quickly recombined or collapse.
According to the present invention, the spherical, particle-shaped
material is thus to show a hydrophilic-hydrophobic balance where
the particle in itself constitutes the hydrophobic part and where
the quantity of non-ionic tenside which can be adsorbed in a stable
way on the surface of the particle constitutes the hydrophilic
part.
According to the present invention, the particle in question can
then consist of a homopolymer or copolymer consisting of styrene
and/or one or a plurality of esters of acrylic or methacrylic acid
with the general formula ##STR1## in which R.sub.1 .dbd.H or
CH.sub.3 and R.sub.2 .dbd.the alcohol radical with 1-8 carbon
atoms, e.g. methyl acrylate, ethyl acrylate, propyl acrylate, butyl
acrylate, hexyl acrylate or 2-ethyl acrylate, methyl methacrylate,
ethyl methacrylate, butyl methacrylate, hexyl methacrylate,
2-ethyl-hexyl methacrylate. With an increased length of the chain
in the alcohol radical, the hydrophobic property increases, and
consideration must be taken to this when choosing the type and
quantity of the hydrophilic component.
According to other variants of the invention, the particle in
question can consist of a copolymer of styrene-butadiene or a
copolymer of acrylate vinylidene chloride or pure vinylidene
chloride or pure polyethylene.
The hydrophobic particle characteristic for the invention can also
be a non-synthetized natural product, and as an example of such a
product may be mentioned asphalt particles with a particle size of
0.1-0.8 .mu.m.
The quantity of tenside which can be adsorbed in a stable way on
the various particles varies somewhat between these with
consideration to the size and hydrophobicity of the particles and
the own hydrophilicity of the tenside.
Through practical tests, it can thus be shown that a surface-active
substance has a stronger affinity towards a polymer, the more
hydrophobic this is. This involves that a very hydrophobic polymer
has the capability of adsorbing a greater quantity of tenside than
a less hydrophobic polymer. Consideration must be taken to this in
connection with the present invention, as a possible tenside
quantity that can be released from the particle-shaped material has
a negative effect on the pore structure of the cement mortar.
Thus, generally speaking, the tenside quantity varies between 0.1
and 5.0 percent by weight, counted on the whole of the
particle-shaped material. For the polymers based on acrylic acid
esters or methacrylic acid esters, and the polymers based on
acrylate-vinylidene chloride, however, there are closer limits,
0.1-3.0 percent by weight. For the more hydrophobic materials
asphalt, polyethylene and styrene butadiene, the wider general
limits of 0.1-5.0 percent by weight are applicable. Further, the
appropriate quantity of tenside within the above-mentioned limits
is dependent on the particle size and type of tenside.
Examples of appropriate non-ionic tensides are oxyethylated alkyl
phenol, where the number of ethylene oxide units has varied from
6-40, polyoxyethylene sorbitan monolaurate with approx. 20 units of
ethylene oxide, polyoxyethylene sorbitan monopalmitate,
polyoxyethylene sorbitan mono-oleate.
As examples of particle-shaped materials that have proved to
function very well may be mentioned acrylic based products with a
particle size of 0.2-0.6 .mu.m and asphalt particles with a
particle size of 0.1-0.8 .mu.m.
In addition to the various methods of producing a fine-pored cement
mortar as above, the present invention also comprises an
application for utilizing a cement mortar produced in this way in
connection with the production of a lightweight aggregate concrete
with a density of less than 1400 kg/m.sup.3 in which the aggregate
material and the adhesive cement mortar have a pronounced different
density, and the aggregate percentage of which exceeds 45-50
percent by volume. By lightweight aggregate is meant in this case
aggregate material with a mean particle density of less than 1200
kg/m.sup.3. In this case, the designation lightweight aggregate
concrete only includes products where the cement mortar, apart from
its own porosity, entirely fills out the space between the
aggregate particles.
It has hitherto proved to be very difficult with the aid of cement
additives available in the market to achieve a coherent and
pourable lightweight aggregate concrete with a aggregate content
exceeding 45-50 percent by volume. The reason for these
difficulties can primarily be ascribed to the great difference in
density between the cement mortar and the lightweight aggregate.
The adhesive forces of the mortar have been too weak to prevent the
lighter aggregate particles from separating and floating up in the
mortar when the fresh concrete is being worked. A concrete with
cavities is then obtained, in which the cavities between the large
aggregate particles are not entirely filled out by the cement
mortar. However, it is more simple to produce concrete with
cavities of this type if, already from the beginning, the quantity
of cement added is limited to only the quantity required for
adhesion between the aggregate particles. Such products, which are
primarily used for cement blocks, are produced today by many
manufacturers.
When a cement block of this type is immersed in water, the spaces
between the large aggregate particles are almost instantaneously
filled with water. Products of the type hollow cement blocks are
not comprised in the invention. They can easily be produced with
conventional cement mortar.
According to the variant of the invention now in question, it has
thus become possible to manufacture a lightweight aggregate
concrete with a density of less than 1400 kg/m.sup.3 containing
preferably 80-140 liters of cement/m.sup.3 concrete, 450-800 liters
of lightweight aggregate/m.sup.3 concrete, 0-100 liters of
sand/m.sup.3 concrete (the sand can be replaced by other material
which may possibly be included in the bonding agent part), 100-180
liters of water/m.sup.3 concrete and 0.2-5.0 percent by weight
counted on the cement weight of the substantially spherical
particles which are chemically inert in relation to the other
components in the mortar, and which have a particle size of 0.1-1.0
.mu.m and also consist of a hydrophobic material which has been
stabilized in the particle shape in question by means of a
non-ionic tenside which has been adsorbed on the surface of the
particles to a content of 0.1-5.0 percent by weight counted on the
quantity of particle-shaped material.
These components together give a composite in which the adhesive
cement mortar through the air drawn in at the mixture has obtained
a density of 1200-2000 kg/m.sup.3 with a pore size of substantially
5-30 .mu.m. However, as a rule, cement mortar with a density of
less than 1600 kg/cm.sup.3 obtains an altogether too low strength
unless the sand fraction comprised in the mortar has been replaced
by some latent hydraulic binding agent such as fly ash, finely
ground granulated blast furnace slag, Puzzolans or the like. We
expect the lightweight aggregate in question to have a particle
density of less than 1200 kg/m.sup.3 and a quantity corresponding
to 40-80 percent by volume. A mixture thus produced, because of the
stability of the air which is mixed in and also the fine
distribution of the excess water in the mortar can be cast in a
conventional way. The stability of the fresh mortar effectively
prevents the aggregate particles from floating up in the mortar
before this has stiffened. The reasons for this have previously
been described in the text.
The spherical, particle-shaped material can consist of the
previously described types.
The present invention has been defined in the accompanying claims,
and will now be somewhat further described in the following
examples.
In examples 1 and 2 and 4-7, the production of various types of
particle-shaped materials which satisfy the conditions indicated in
the patent claims are indicated, and example 3 describes the
production of a particle-shaped material which because of its high
tenside content does not fulfil these conditions.
Examples 8-14 refer to a cement mortar and lightweight aggregate
concrete produced according to the method characteristic for the
invention.
EXAMPLE 1
A 2-liter 3-necked flask provided with stirrer, reflux cooler,
thermometer and intake for nitrogen gas was charged with 600 g
distilled water, 4 g oxyethylated nonyl phenol with 20 units of
ethylene oxide, 64 g styrene, 16 g 2-ethyl hexyl acrylate and 0.7 g
ammonium persulphate. The temperature was raised to 83.degree. C.,
and a polymerization was obtained. The temperature rose to
91.degree. C. The charge was cooled to 85.degree. C. and 1 g
oxyethylated nonyl phenol with 20 units of ethylene oxide, 64 g
styrene, 16 g 2-ethyl hexyl acrylate, 0.2 g ammonium persulphate
were added. A reaction was obtained, and the temperature rose to
92.degree. C. The procedure according to step 2 was repeated 3 more
times. After the reaction of step 5, the temperature was held at
80.degree. C. for 1 hour, followed by cooling to 25.degree. C.
Water in steps (2-5) was used for dissolving of the emulsifier and
the initiator. Table of quantities charged as above.
Table 1
__________________________________________________________________________
(weights given in g) Step 1 Step 2 Step 3 Step 4 Step 5
__________________________________________________________________________
Distilled water 600 2 2 2 2 Oxyethylated nonyl phenol 20EO 4 1 1 1
1 Styrene 64 64 64 64 64 2-ethyl hexyl acrylate 16 16 16 16 16
Ammonium persulphate 0.7 0.2 0.2 0.2 0.2 The particle size of the
polymer particles produced at the reaction described above was
determined in a sweep electron microscope to be 0.25-0.35 .mu.m The
dry substance of the dispersion obtained was 40%
__________________________________________________________________________
EXAMPLE 2
The procedure according to example 1 was repeated, but with the
difference which will be noted from the following table.
Table 2 ______________________________________ (weights given in g)
Step 1 Step 2 Step 3 Step 4 Step 5
______________________________________ Distilled water 600 2 2 2 2
Polyoxyethylene sorbitan monolaurate with 20EO 2 0.5 0.5 0.5 0.5
Methyl methacrylate 48 48 48 48 48 Butyl acrylate 32 32 32 32 32
Ammonium persulfate 0.7 0.2 0.2 0.2 0.2 Particle size deter- mined
in scanning microscope 0.45 .mu.m Dry substance 39.8
______________________________________
EXAMPLE 3
The procedure according to example 1 was repeated, but with the
difference which will be noted from the following table. Reaction
temperature 40.degree.-52.degree. C.
Table 3 ______________________________________ (weights given in g)
Step Step Step Step Step 1 2 3 4 5
______________________________________ Distilled water 528 18 18 18
18 Oxyethylated nonyl phenol with 10 EO 6 6 6 6 6 2-ethyl hexyl
acrylate 72 72 72 72 72 Methyl methacrylate 46 46 46 46 46 Acrylic
acid 2 2 2 2 2 Ammonium persulfate 0.6 0.6 0.6 0.6 0.6
Na-pyrosulfite 0.4 0.4 0.4 0.4 0.4 Particle size determined in
Scanning microscope 0.2-0.25 .mu.m Dry substance 50.5%
______________________________________
EXAMPLE 4
140 g granulate of polyethylene was charged into a 3-necked flask
provided with reflux cooler, stirrer and thermometer and heated to
125.degree. C., and the polyethylene then melted. 5.6 g
oxyethylated octyl phenol with 40 units of ethylene oxide was
charged and stirred 5 minutes. To 828 g water which had been heated
to 95.degree.-100.degree. C. the melt described above was charged
with vigorous stirring. The temperature was held at 90.degree. C.
for 0.5 hours, followed by cooling.
______________________________________ Particle size determined in
scanning microscope 0.2-0.7 .mu.m Dry substance 54.0%
______________________________________
EXAMPLE 5
160 g water, 180 g asphalt with a softening point of
48.degree.-56.degree. C. (ASTM D-36) and 8.1 g polyoxyethylene
sorbitan monostearate with 30 units of ethylene oxide was heated
under pressure to 125.degree. C. with intensive stirring, and an
asphalt emulsion was then obtained. Cooling to room
temperature.
______________________________________ Particle size determined in
scanning microscope 0.2-0.7 .mu.m Dry substance 54.0%
______________________________________
EXAMPLE 6
A non-carboxylated styrene-butadiene dispersion was dialyzed to
remove the tenside adsorbed on the particles. The dry content was
determined, and to 100 g polymer substance, 3.5 g oxyethylated
lauryl alcohol with 10 units of ethylene oxide was added during
stirring.
______________________________________ Particle size determined in
scanning microscope 0.28-0.37 .mu.m
______________________________________
EXAMPLE 7
A dispersion based upon vinylidene chloride and butyl acrylate was
dialyzed to remove the tenside adsorbed on the particles. The dry
content was determined, and 1 g oxyethylated cetyl alcohol with 20
units of ethylene oxide was added during stirring.
______________________________________ Particle size determined in
electron microscope 0.3-0.4 .mu.m
______________________________________
EXAMPLE 8
(A) Standard Portland cement without aggregate additive was stirred
in water in a laboratory mixer for cement testing. In order to
obtain a coherent cement paste a minimum added quantity of water
corresponding to a water cement ratio of 0.23 was required.
(B) The test according to A was repeated with the difference that
1.2 percent by weight counted as dry product of the particle
described in example 2 was added dispersed in the water mixed in.
In this case, a water cement ratio of approx. 0.18 was required in
order to obtain substantially the same consistency as according to
A.
(C) A pure cement paste was prepared according to A, but with the
difference that the water cement ratio this time was 0.35.
When the paste had been allowed to rest a few minutes, water began
to be separated on the surface of the paste, i.e. bleeding
occurred.
(D) A cement paste prepared according to B, but with a water cement
ratio of 0.35 did not show any tendency whatsoever towards bleeding
during the time until the cement hardened.
The tests show that with the method characteristic for the
invention the water required for the same consistency can be
reduced, and the tendency towards bleeding can be reduced in a pure
cement paste.
EXAMPLE 9
A cement mortar with the following composition was prepared
according to the Swedish regulations for cement testing:
______________________________________ 500 g standard Portland
cement 500 g standard sand 0-0.5 mm 500 g " 0.5-1 mm 500 g " 1-2 mm
250 g water ______________________________________
The pore structure in this standard mortar was modified in the way
indicated below.
(A) Through the addition of the quantities indicated in table 4,
counted as dry polymer, of the acrylic dispersion described in
example 2, the changes in the density of the mortar indicated in
the table were obtained.
Table 4 ______________________________________ Percental additive
counted on weight of cement 0 1 2 4
______________________________________ Density of mortar when fresh
kg/m.sup.3 2140 2000 1860 1650 Percental increase of air volumes 0
6 13 22 ______________________________________
A characteristic feature of the air mixed in was its stable binding
in the structure. The air pores formed had a diameter substantially
within the range of 5-30 .mu.m. the pore structure was studied in a
sweep electron microscope. The strong binding of the air pores in
the mortar will be noted from the fact that the air content was not
noticeably changed when the mortar was vibrated on a vibro table
for up to 10 minutes.
EXAMPLE 10
The procedure according to example 9 was repeated with particles
according to examples 1, 3, 4, 5, 6 and 7. Density given in
kg/m.sup.3.
Table 5 ______________________________________ Percental additive
counted on weight of cement 1 2 4
______________________________________ Particles according to
example 1 2000 1840 1630 example 3 1600 1550 1480 example 4 1950
1840 1650 example 5 1890 1800 1530 example 6 1900 1810 1620 example
7 1870 1780 1510 ______________________________________
A characteristic feature of the mortar to which particles according
to examples 1, 4, 5, 6 and 7 had been added was that the air mixed
in was very stable. The air content was not changed when the mortar
was vibrated on a vibro table for 10 minutes. The particles
according to example 3, when the corresponding quantity had been
added, had a good air admixing effect, but the mortar obtained
showed poor cohesion at vibration, and a tendency towards
separation. Further, the air content was changed. The mortar to
which particles according to 1, 4, 5, 6 and 7 had been added proved
to have air pores within the range of 5-30 .mu.m while the mortar
according to example 3 contained air pores within the range of
50-250 .mu.m.
EXAMPLE 11
In a concrete mixer, a lightweight aggregate concrete with the
following composition was prepared.
______________________________________ Kg Liters
______________________________________ Cement (standard Portland)
350 112 Lightweight aggregate 1805 mm.sup.x 200 Lightweight
aggregate 24010 mm.sup.x 400 Sand 0-2 mm 265 100 Water 150 150
______________________________________ .sup.x Lightweight aggregate
of type ball-sintered clay.
Lightweight aggregate 5-12 mm, lightweight aggregate 0-5 mm, cement
and sand were charged in the order mentioned, followed by dry
mixing for 1 minute. Water together with particles, the quantity
and type of which will be noted from the summary below, was added
and mixed for 3 minutes. The concrete was poured into an open mould
and vibrated. The following judging scale was used for the casting
tests.
Casting properties and cohesion
1=No cohesion whatsoever. At vibration, mixture segregates and
lightweight aggregate leaves the system.
2=Certain cohesion, but tendency towards separation can be
noted.
3=Very good cohesion, no tendency towards separation.
Consistency
For the measuring of the consistency in lightweight aggregate
concrete, a method is proposed which is described in the German DIN
standard (1048-1972). The equipment consists of a spreading table
70.times.70 cm. The table should have a weight of 16 kg and one
edge should have a lifting height limited to 4 cm.
On the table, a truncated cone of concrete is formed using a mould
with a height of 20 cm and an upper and lower diameter of 13 and 20
cm. The mould is set on the middle of the table and the concrete is
compressed with a rod. The cone is filled in two layers of equal
height, and each layer is packed with 10 blows with the rod. The
mould is removed from the cone after one-half minute. Thereafter,
with the aid of the handle, the table is allowed to fall within the
working range 15 times during 15 seconds. The spreading is
thereafter measured in two directions at right angles and is
indicated in cm. The cohesion and separation tendencies of the
concrete can also be determined ocularly.
______________________________________ % additive counted on cement
weight Cohesion Type of (solid sub- Consistency Casting additive
stance) (spread in cm) properties
______________________________________ -- 0 X 1 Particles according
to Example 1 1.2 31-33 3 " 1.5 33-35 3 " 3.5 35-37 3 Particles
according to Example 2 0.9 29-31 3 " 1.3 32-34 3 Particles
according to Example 3 1.0 33-35 1.5-2 particles according to
Example 5 0.8 28-30 3 " 1.1 31-33 3 Particles according to Example
4 1.6 33-34 3 Barra 55L 0.15 35-36 1 Barra 55L 0.6 36-37 1 UCR 0.03
33-34 1 Sodium lauryl sulfate 0.4 36-38 1 Adduct ethylene oxide
nonyl phenol (20EO) 0.5 34-37 1 Adduct ethylene oxide lauryl
alcohol (10EO) 1.0 33-36 1 ______________________________________
BARRA 55L is a commercial product marketed as an air entraining
agent. It function is primarily to be considered to be of the
tenside type. Recommended quantities to be added are at 50 cm.sup.3
/100 kg cement, i.e approx. 0.5.degree./oo. UCR is a commercial
product which is considered to give a mortar with better cohesion
(water thickener) and thereby prevent separation between mortar and
ballast. The main component in UCR is considered to be polyethylene
oxide.
Consistency is changed immediately at the use of Barra 55 L, the
tensides described and particles according to the invention. This
appears in the form of an increased spread at the test of the
consistency. No cohesive effect whatsoever was obtained at the use
of Barra, UCR or tensides. Particles according to example 3 with
the higher tenside content compared with particles according to the
invention tended to be better, but proved to have a comparatively
larger air pore size. The poor cohesion must be ascribed to the
high tenside content and the carboxyl content of the particles,
which gives poorer affinity of the tenside to the particle.
Examples 12-14 describe different lightweight aggregate
compositions with a constant volume of light ballast (65 percent by
volume) and a varying quantity of cement in the mortar. The
compositions used in the respective examples tested will be noted
from the following tables. Without extra additives, all of the
mixtures were considered to be difficult to cast.
EXAMPLE 12
______________________________________ Kg Liter
______________________________________ Cement 250 80 Lightweight
aggregate 0-3 mm 175 163 Lightweight aggregate 3-20 mm 195 325
Lightweight aggregate 10-20 mm 85 162 Sand 0-2 mm 239 90 Water
.apprxeq.180 .apprxeq.180
______________________________________
EXAMPLE 13
______________________________________ Kg Liter
______________________________________ Cement Std 314 100
Lightweight aggregate 0-3 mm 175 163 Lightweight aggregate 3-10 mm
85 162 Sand 0-2 mm 186 70 Water .apprxeq.180 .apprxeq.180
______________________________________
EXAMPLE 14
______________________________________ Kg Liter
______________________________________ Cement Std 377 120
Lightweight aggregate 0-3 mm 175 163 Lightweight aggregate 3-10 mm
195 325 Lightweight aggregate 10-20 mm 80 162 Sand 0-2 mm 133 50
Water .apprxeq.180 .apprxeq.180
______________________________________
The fresh mixtures were thereafter modified according to the method
characteristic for the invention by the addition of the
particle-shaped material described in example 1. Various quantities
between 0 and 2% additive were tested. With an increased cement
content and quantity of additive, better casting properties were
obtained. The pressure strength of the compositions tested was
checked after 28 days, at the same time as the bulk density was
determined.
The values then measured are shown in the diagrams in FIGS. 1 and
2. All of the values refer to well compacted mixtures. The water
cement ratio of the various compositions is shown in FIG. 3. In
FIG. 1, ranges I, II and III have been indicated. These show the
approximate limits for
Range I: concrete which cannot be cast
Range II: concrete which can be cast but which, however, can
segregate, i.e. a separation of the aggregate can take place.
Range III: concrete which can be cast without any tendencies
towards segregation.
From FIGS. 1 and 2 it will be noted that with small contents of
additives within range I, particularly with small quantities of
cement, a remarkably low bulk density is obtained. This is
explained by the great inner friction of these mixtures, which
prevents a compression of the cast mass. The low density thus
refers to the comparatively large compression pores, and not the
finely distributed mixed-in air.
* * * * *